This invention relates to surface acoustic wave device testing and in particular to nondestructive testing of interdigital transducers on surface acoustic wave device substrates.
Surface acoustic wafe devices often represent desirable new or improved alternate technology used for electrical filtering, generation and analog computing in such applications as radar, information processing and guidance systems. It is therefore desirable that there be developed a capability for rapid, inexpensive and accurate testing of surface acoustic wave transducers and other SAW components produced for use in Air Force and other systems. It is also desirable that techniques developed be adaptable to studying charge distributions which exist on interdigital fingers under various electrical operating conditions for the purpose of improving device design.
Presently it is extremely difficult if not impossible to detect all defects which will cause faulty or degraded operation of SAW transducers optically (or through the use of scanning electron microscopy) or by electrical testing.
The present invention is a test method that overcomes these deficiencies and solves the problem of determining if a SAW transducer has any defective fingers. It does this nondestructively so that the method can be used as a production line screen test during the SAW device manufacturing process before the device is assembled into a package. The test method allows determination based on a simple optical inspection of whether the SAW transducer tested contains defects which cause portions of interdigital electrode fingers to be electrically poorly connected or not connected to their respective external device terminals. It allows that determination without the need to functionally test the SAW device in a conventional manner or even to mount the device in a suitable package with external electrical connections. The required electrical connections can be made using external probes. The packaging and functional testing of SAW devices is very expensive and time consuming compared to the method of the invention. The method of the invention may also be useful in studying charge distributions which exist on fingers under various electrical operating conditions for the purpose of improving device designs.